Electric control circuit



Dec. 28, 1943.

G. L. ROGERS 2,337,933

ELECTRIC CONTROL CIRCUIT Original Filed Oct. 31, 1941 2 Sheets-Sheet 1 10 v z/ J] 43 v '40 5/ 47 49 32 V 4/ 35 39 A 4s Dec. 28, 1943. ROGERS 2,337,933

ELECTRIC CONTROL CIRCUIT Original Filed Oct. 31, 1941 3 Sheets-Sheet 2 Fig. 5.

WHEN 32, 34 AND35 /(ARE OMITTED.

Fig.7.

WHEN 40,43 AND 44-, ARE oMn'TEDA x r 5- c I Inventor: George Lfiogers, by JVa my T '5 M His Attorney Patented Dec. 28, 1943 ELECTRIC CONTROL CIRCUIT George L. Rogers, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Orig nal application October 31, 1941, Serial No. 417.352. Divided and this application April 14, 1943, Serial No. 482,985

7 Claims.

My invention relates to electric control circuits and more particularly to improved electric circuits for producing a control voltage of predetermined characteristics from a source of voltage having a different characteristic. This application is a division of my copending application, Serial No. 417,352, filed October 31, 1941, and assigned to the assignee of this application.

It is often desirable to produce a voltage which varies in magnitude at different rates or in different directions for diiierent portions of a complete range of variation of a supply voltage which may, for example, vary uniformly in one direction. If the supply circuit is controlled to produce a unidirectional voltage which increases steadily in magnitude, it may be desirable to produce a control voltage which increases steadily for a portion of the range of increase of supply voltage; remains constant for a second portion of the range of increase of supply voltage; and decreases through a third portion of the range of increase of supply voltage. In accordance with the teachings of my invention, I provide an improved control circuit for producing a control voltage the magnitude of which varies in different directions during different ranges of variation of a supply circuit voltage in one direction.

It is an object of my invention to provide new and improved electric control circuits.

It is another object of my invention to provide a new and improved control circuit for producing a control voltage from a supply voltage of variable magnitude which remains constant or varies in opposite directions as the supply voltage is varied progressively in one direction.

Briefly stated, in the illustrated embodiments of my invention, I have shown my invention applied to circuits for producing excitation voltages for the electric valves of a phase-shifting circuit from sources of unidirectional voltage, the magnitudes of which are increased progressively in one direction.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. Fig. 1 of the drawings illustrates my invention as applied to a phase shifting arrangement for controlling the phase of the voltage applied to a single phase output or load circuit from a polyphase alternating cur rent. supply circuit. Fig. 2 represents an aspect of the control circuit shown in Fig. 1. Fig. 3 represents certain operating characteristics relative to the control of the respective pairs of electric discharge devices shown in Fig. 1. Figs. 4, 6 and 8 represent in detail portions of the respective excitation circuits connected to the three groups of electric discharge devices shown in Fig. 1; and'Figs. 5, '7 and 9 represent certain operating characteristics of the control or excitation circuits shown in Figs. 44, 6 and 8. respectively. Fig. 10 represents a complete arrangement wherein the excitation circuits are shown connected to the phase shifting arrangement of Fig. 1.

Referring now to the arrangement shown in Fig. l, I have there illustrated my invention as applied to a phase shifting circuit for controlling the phase of the voltage applied to an output circuit l which may include a transformer 2. The phase shifting circuit may he energized from a polyphase alternating current supply circuit 3 and includes a plurality of n electrically displaced phase windings. Although not limited thereto, 1 have illustrated my invention as applied to a system which is energized from a three phase alternating current supply circuit and in which the electrically displaced windings are pro vided by a transformer 4 having a plurality of primary windings 5 and a plurality of electrically displaced secondary or phase windings 6, l and 8 having an electrically intermediate or neutral connection 9 which is connected to one terminal of the output circuit.

The phase shifting circuit also includes a plurality of variable impedance means such as n pairs of reversely connected electric discharge devices H], H; l2, I3; I4, [5 which are connected to phase windings 6, I and B, respectively. Electrio discharge devices l0-l5, inclusive, are preferably of the high vacuum type each including an anode IS, a cathode ll and a control member or grid 58. The grids E8 of the discharge devices are connected to excitation circuits described in detail hereinafter and which are represented in Fig. 1 as comprising circuits l9, 2!! and 2| It will be noted that the common juncturcs of the respective pairs of electric discharge devices are connected to one terminal of the load or output circuit l.

I connect between the excitation circuits l 9, Eli and 2! and the respective associated pairs of electric discharge devices transformers 22, 23 and it to control the conductivities of these discharge devices so that the pairs operate as an equivalent variable resistance in response to the variations in the grid voltages applied thereto. It will be noted that each of the discharge devices in the respective pairs is connected reversely, that is, having the anode of one connected to the cathode of the other, in order to transmit both half cycles of alternating current of the respective associated phase windings. Transformers 22-44 are preferably arranged to have a 1:1 ratio, thereby serving to maintain the grid and cathode of elec tric discharge devices Ill, I2 and I4 at the same potential so that only the unidirectional excitation is effective. In this manner, the alternating Component o Voltage due to the connection to the anode-cathode circuit is effectively neutralized so far as each of the grid control or excitation circuits is concerned. Fig. 2 represents a portion of the circuit shown in Fig. 1 in which the aspects of the neutralization, by using the transformer connections of this nature, are more succinctly represented. It will be noted that the secondary winding 25 is connected across the grids I8 of electric discharge devices In and II, and that the primary winding 26 is connected to the common junctures of the cathodes of the discharge devices. In this manner, the alternating components of voltage which are present in the anode-cathode circuits of the pairs of discharge devices is effectively eliminated from the grid circuits so that the discharge devices respond precisely to the magnitude of the unidirectional voltages of the control circuits.

The control circuits or excitation circuits I9- 2| which I provide for selectively controlling the conductivities of the discharge devices IIl-I5, inclusive, include means, specifically described hereinafter, which are selectively responsive to a unidirectional control voltage and selectively control the conductivities of the different pairs in different manners in response to different magnitudes of the unidirectional control voltage. I provide this type of control in order to vary or control the phase of the output voltage supplied to output circuit I. For example, I have found that if the conductivity of one of the pairs of electric discharge devices, such as discharge devices III and II, is maintained substantially constant or at a zero value, the phase of the voltage supplied to the output circuit I may be varied throughout electrical degrees by increasing the conductivities of the discharge devices I2 and I3 and decreasing the conductivities of the discharge devices I4 and I5. Furthermore, by progressing this sequence type of control to other groups of electric discharge devices, the phase of the voltage supplied to the output circuit may be shifted throughout an additional n electrical degrees and, lastly, by choosing another combination of discharge devices controlled in a corresponding manner, the shift in phase may be made throughout another electrical degree interval thereby completing the phase shift throughout the complete 211- or 360 electrical degrees.

The diagram of Fig. 3 may be of assistance in explaining the manner in which the respective pairs of electric discharge devices shown in Fig. 1 may be controlled to obtain any desired shift in phase of the voltage supplied to output circuit I. If the voltages of the excitation circuits I9, 2!) and 2| be represented by the characters Ex, Ey and Ez, respectively, and if it be assumed that the electric discharge devices are of the type which are rendered completely nonconducting by impressing on the grids I8 thereof a 5 volts, the relation of the shift in phase and the respective grid voltages may be represented by the curves shown in Fig. 3. By referring to these curves, it will be noted that during any one interval of time the conductivity of one pair of discharge devices is reduced to zero by impressing thereon a negative hold-01f voltage of 5 volts and by concomitantly varying the conductivities of the other two pairs of electric discharge devices.

Figs. 4, 6 and 8 represent the excitation circuits which are connected to circuits I9, 20 and ZI, respectively, of Fig. 1. These excitation circuits are energized from a common control circuit including a positive conductor 27 and a negative conductor 28, and the voltage of Which is represented by the character E1. These circuits are selectively responsive to the magnitude of the unidirectional voltage E1 and control the magnitude of the bias voltages impressed on the grids I8 of the respective associated pairs of electric discharge devices.

Considering Fig, 4;, I there provide an arrangement in which the voltage applied to circuit I9 varies in the manner indicated by the solid curve A of Fig. 5. It will be noted that the bias voltage Ex increases to a negative maximum value upon increase of voltage E1 to a predetermined value, and that the bias voltage remains substantially constant through a second region or range until the voltage E2 attains a second predetermined value, and that the bias voltage progressively decreases in magnitude upon further increase of E1 beyond the second predetermined value.

In order to obtain this type of control, I provide in Fig. 4 a circuit including a voltage divider comprising a pair of serially connected resistances 29 and 30 having a common juncture 3| which is connected to one conductor of circuit I9. To impress on circuit IS a voltage which is zero when E1 is zero and which progressively and linearly increases in magnitude until E1 attains a predetermined value, I provide resistances 32 and 33 in series relation connected between the nega tive conductor 28 and one terminal of circuit I8. As the voltage E1 increases, a proportionate voltage is transmitted to circuit 59. The component of voltage so transmitted is determined, of course, by the ratio of resistances 29 and 30. I have found that these resistances may, if desired, be made equal so that one-half the voltage E1 is available for the control of the circuit I9. To maintain the voltage of circuit I9 substantially constant for the second range of voltage E1, I employ a source of reference voltage, such as a battery 34 and a unidirectional conducting device 35, which are oppositely poled and connected to transmit current through resistances 39 and 32 when the voltage appearing across resistance 30 attains a value corresponding to the first predetermined value of E1. Throughout the second range of E1, the unidirectional conducting device 35 transmits current through resistances 3B and 32 to maintain the voltage transmitted to circuit I9 at a substantially constant value. I provide a second source of reference voltage, such as a battery 36 and a unidirectional conducting device 31, which are oppositely poled and connected in series relation between the positive conductcrzl and-the resistance 33 to decrease progressively the 'magnitude of the bias voltage when E1 increases in magnitude beyond the second predetermined value.

It will be understood that the operating characteristics shown in Fig. represent the theoretical shape of the curve which would be obtained by assuming that no'voltage appears across the unidirectional conducting devices. However, in asmuch as the devices necessitate the impression of a predetermined voltage thereacross, it will be appreciated that the curves actually when plotted from observed data will have scnewlciat-rounded portions instead of the sharp characteristics shown. The upper dotted portion Of the char-- acteristics shown in 5 may be obtained and the characteristics changed by omitting the source of reference voltage or battery resistance 32 and device s i;

The operation of thearrangernent shown in Fig. 4 will be explained by considering the circuit upon a progressive increase in magnitude of E1. During the first range of E1, the voltage applied to circuit it increases progressively and linearly clue to the rise in voltage across resistance 5%. Upon attaining a predetermined value and for voltages within a predetermined range above that value, the voltage drop across resistance is sufficient to overcome the voltage of battery 3%, causing current to flow in a circuit including battery 34, device resistance 35 and resistance 32. The voltage drop appearing across res'stance 32 is sufficient to neutralize counteract the rise in voltage appearing across resistance 36 occasion d by increase of voltage E1, thereby maintaining the voltage supplied to circuit l9 substantially constant throughout a second range of E1. When the voltage of E1 increases to a second predetermined value, causing unidirectional conducting device 3? to conduct current, the magnitude of the voltage transmltted'to cir cuit i9 is progressively decreased. During this region of operation current is conducted by battery 3%, device ill, and resistances t3 and Upon a decrease of E1, curve A is traversed in the reverse direction. 7

Control circuit 26, shown detail in Fig. 6, is constructed to produce a voltage having the characteristic of curve B in Fig. '1. In this arrangement I provide a source of voltage, such as a battery stand resistances and' iil which transmit a voltage of predetermined value to circuit 2!) when the value of E1 is zero and which progressively decreases the magnitude of the voltage supplied to circuit 2 for increase of E1 with.- in the first range of E1 by transmission of current through resistances and ill. When E1 attaines the predetermined value, the voltage supplied to circuit Eli is reduced to zero and upon a further increase of voltage of E1 into the sec-- ond range I provide a unidirectional conducting devices! and a source of reference potential,

such as a battery it, which conduct greater amounts of current through resistance '39 to increase progressively the magnitude of the bias voltage Ey until the voltage E1 attains a second predetermined value. As a means for limiting the magnitude of the voltage supplied to circuit 2i] upon increase of E1 beyond the second predetermined value, I connectacrcss circuit 20 a unidirectional conducting device and source of reference voltage such as a battery as.

The voltage E may be made to have the characteristic shown bythe: dotted. line withinthe third region or rangectoperationby omitting resistance M, unidirectional conducting device 43 and the source of voltage 44.

The circuit of Fig. 8 produces an output characteristic corresponding to curve C of Fig. 9. In this arrangement the voltage applied to circuit 2! is maintained substantially constant throughout the first range of E1 by meansof a source of voltage 45 and resistances 4t and ll. When E1 attains a predetermined value, the magnitude of the bias voltage supplied to circuit 2! is progressively decreased throughout a second predetermined range of E1 by means of a source of reference voltage 28 and unidirectional conducting device 49 which complete a circuit through resistance it and source 45. When E1 attains a second predetermined value, the voltage supplied to circuit ii is then progressively increased in magnitude by the provision of a source of reference voltage 5% and a unidirectional conducting device 5i which are connected in the manner shown from one terminal of circuit 26 to the negative conductor Throughout this third mentioned range when the voltage E1 attains or exceeds the second predetermined value, the voltage supplied to the circuit 2! is progressively increased due to the flow of current through devicefil and source The voltage Ez may be made to have the characteristic indicated by the dotted line within the first range of voltage E1 by omitting source 35, resistance M and unidirectional conducting device 69.

Although not limited to the particular range of applied voltages and output voltages, I have found that the circuits shown in Figs. 4, 6 and 8 operate very satisfactorily when the respective elements have the following values:

E1 range from zero to 39 volts Ez=l5 volts Resistance 2$i=resistance 38 Fig. 1.0 shows the circuit of Fig. 1 in combination with the excitation circuits of Figs. 4, 6 and 8 as connected to the respective associated pairs of electric discharge devices in order to obtain the variation in conductivities, represented by the curves of 3, in response to variations in magnitude of the voltage-E1. As the voltage E1 progressively increases from zero to the first predetermined value, that is in the first range, discharge devices it and are maintained nonconducting and the conductivities of electric discharge devices EZ and it are progressively increased and the conductivities of discharge devices ill and ll are decreased, thereby shifting the voltage applied to the output circuit l through electrical'degrees. Throughout the second range of voltage E1, the discharge devices I 0 and H are maintained nonconducting, and the conductivities of electric discharge devices it i and it are progressively decreased, and the conductivities of discharge devices M and i5 are progressively increased. Throughout the third range, discharge devices it and it are maintained nonconducting and the conductivities of devices it ii are progressively decreased and the conductivities of discharge devices H1 and II are progressively increased to provide an additional 129 degree shift in phase. In this manner, the phase of the voltage impressed on the output circuit may be smoothly controlled throughout three consecutive or adjacent 120 electrical degree intervals, and the phase displacement of the output voltage may be accurately controlled or determined by the magnitude of the voltage E1 which is impressed on all three of the excitation circuits. Upon decrease in the magnitude of voltage E1, the output voltage is shifted in the opposite direction.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a direct current circuit for producing a variable unidirectional voltage, a voltage divider connected across said source and comprising a resistance having an intermediate connection, an electric circuit connected in circuit with one terminal of said direct current ci cuit and said intermediate connection, means connected to said electric circuit comprising a source of reference voltage, a resistance and a unidirectional conducting device connected in series across one of said resistances to permit an increase of the voltage applied to said electric circuit for variations of said variable voltage to a predetermined value and for maintaining the voltage applied to said electric circuit at a sub stantially constant value for variations in voltage exceeding said value.

2. In combinationa direct current circuit for producing a variable unidirectional voltage, a voltage divider connected across said source and comprising in series relation a pair of resistances, an electric circuit connected in circuit with one terminal of, said direct current circuit and the common juncture of said resistances, a source of reference voltage, a third resistance and a unidirectional conducting device connected in series relation between said juncture and said one terminal to permit an increase of the voltage applied to said electric circuit for variations of said variable voltage to a predetermined value and for maintaining the voltage applied to said electric circuit at a substantially constant value for variations in said variable voltage within a range extending from said first mentioned predetermined value to a second predetermined value, and a second source of reference voltage, a resistance and a unidirectional conducting device connected in series relation between the other terminal of said direct current circuit to said one terminal of said electric circuit through said third resistance for reducing the voltage applied to said electric circuit for values of said variable voltage exceeding said second predeter- -mined value.

tween said juncture and said one terminal to increase the voltage applied to said electric circuit fol-variations of said variable voltage to a predetermined value and for maintaining the voltage applied to said electric circuit at a substantially constant value for variations in said variable voltage within a range extending from said first predetermined value to a second value and a source of reference voltage, a resistance and a unidirectional conducting device connected in series relation from the other terminal of said control circuit to one terminal of said electric circuit for reducing the voltage applied to said electric circuit for values of said variable voltage exceeding said second predetermined value.

4. In combination, a direct current circuit for producing a variable unidirectional control voltage, a voltage divider comprising a pair of serially connected resistances connected across said direct current circuit, an electric circuit having a terminal connected to the common juncture of said resistances, a source of reference voltage and a resistance connected in series relation with one of the first mentioned resistances for supplying to said electric circuit a voltage having a predetermined value when the value of said variable unidirectional voltage is zero, a second source of reference voltage, a resistance and a unidirectional conducting device connected across said direct current circuit for increasing the voltage applied to said electric circuit for variations in said variable unidirectional voltage from said predetermined value to a second predetermined value, and a third source of reference voltage and a unidirectional conducting device connected across said electric circuit for limiting the voltage applied to said electric circuit for values of said variable unidirectional voltage exceeding said second predetermined value.

5. In combination, a control circuit for producing a variable control voltage, a voltage divider comprising a pair of serially connected resistances connected across said control circuit, an electric circuit having a terminal connected to the common juncture of said resistances, a source of reference voltage, and a resistance connected in series relation with one of the first mentioned resistances for supplying to said electric circuit a voltage having a predetermined value when the control voltage is zero, a second source of reference voltage, a resistance and a unidirectional conducting device connected across said control circuit for increasing the voltage applied to said electric circuit for variations in said variable voltage from said predetermined value to a second predetermined value, and a third source of reference voltage and a unidirectional conducting device connected across said electric circuit for limiting the voltage applied to said electric circuit for values of said variable voltage exceeding said second predetermined value.

6. In combination, a direct current circuit for producing a variable unidirectional voltage, a voltage divider connected across said direct current circuit and comprising a pair of serially connected resistances, an electric circuit connectedvto the common juncture of said pair of resistances, means comprising a source of reference voltage connected to said electric circuit, a second source of reference voltage, a resistance and a unidirectional conducting device connected across one of the first mentioned resistances for decreasing the voltage applied to said electric circuit when said variable unidirectional voltage attains a predetermined value and for decreasing the magnitude of the voltage applied to said electric circuit within a region extending from said predetermined value to a sec- 0nd predetermined value, and a third source of reference voltage, a resistance and a unidirectional conducting device connected in series relation between the first mentioned device and one terminal of said direct current circuit for increasing the voltage applied to said electric circuit for values of said variable unidirectional voltage exceeding said second predetermined value.

'7. In combination, a control circuit for producing a variable control voltage, a voltage divider connected across said control circuit and comprising a pair of serially connected resistances, an electric circuit connected to the common juncture of said pair of resistances, means comprising a source of reference voltage connected to said electric circuit, a second source of reference voltage, a resistance and a unidirectional conducting device connected across one of the first mentioned resistances for decreasing the voltage applied to said electric circuit when said control voltage attains a predetermined value and for decreasing the magnitude of the voltage applied to said electric circuit Within a region extending from said predetermined value to a second predetermined value, and means for increasing the voltage applied to said electric circuit for values of said control voltage exceeding said second predetermined value comprising a third source of reference voltage, a resistance and a unidirectional conducting device connected in series relation between one terminal of said control circuit and one terminal of said electric circuit.

GEORGE L. ROGERS. 

